You can use Eraser Portable by plugging in your portable device on any computer and use it just like you would on your own computer.

It is a repackaged version of the popular Eraser utility designed with portability in mind, so it has all the same great features of Eraser, but there's nothing to install.

Features
Eraser Portable is a secure file-deletion and data wiping utility. With support for multiple wipes, pattern writing and more, it can be used to securely delete any sensitive data.

Flash Drive Note: Most modern flash drives use wear leveling to spread write operations out over a device. This interferes with Eraser (and other secure deletion utilities) ability to wipe single files. Wiping an entire drive or erasing a file and then wiping free space should still work securely, though it will put additional wear on your drive.